| Inhealth Intelligence Limited | Health & social care | 1996 |
| Inhealth Limited | Health & social care | 2004 |
| Inhealth Pathology Limited | Health & social care | 2016 |
| Inhealth Properties Limited | Real estate | 2004 |
| Inhealth UK Holdings Limited | Professional & scientific | 2009 |
| Inhealth Ventures GP LLP | | 2022 |
| Inhealth Ventures L.P. | | 2023 |
| Inhealth Ventures Limited | Professional & scientific | 2016 |
| Innoscite Limited | Professional & scientific | 2013 |
| Innovation 1ST Limited | Professional & scientific | 2022 |
| Innovimpact Ltd | Professional & scientific | 2014 |
| Innvest Limited | Construction | 2019 |
| Innvest W Freehold Ltd | Real estate | 2025 |
| Innvest W Ltd | Real estate | 2024 |
| Inpro Properties LLP | | 2008 |
| Inside OUT Thinking Limited | Other services | 2022 |
| Inspectra Ltd | Professional & scientific | 2024 |
| Inspirai Healthcare Ltd | Professional & scientific | 2024 |
| Instant Construction Ltd | Administrative & support | 2014 |
| Instant Impact Training Ltd | Professional & scientific | 2018 |
| Institutional Money Market Funds Association Limited | Other services | 2000 |
| Intagroup Properties Limited | Extraterritorial | 1978 |
| Intelliheat Solutions Ltd | Professional & scientific | 2013 |
| Interclad Associates Limited | Construction | 2008 |
| Interclad Cyprus Ltd | Construction | 2018 |
| Interclad Firebrand Ltd | Construction | 2018 |
| Intercruit Limited | Administrative & support | 2022 |
| INTERCRUIT25 Ltd | Construction | 2024 |
| Interium Limited | Professional & scientific | 2023 |
| Intermorphic Limited | Information & communication | 2007 |
| International Brokerage & Trading Services (Ibts) Ltd | Wholesale & retail | 2021 |
| International Illuminance Services Limited | Professional & scientific | 2011 |
| International Venue Management Limited | Professional & scientific | 2016 |
| Intrinsic Designs Ltd | Real estate | 2005 |
| Investment Consultancy Partnership Limited | Financial services | 2021 |
| Invincible Properties Limited | Real estate | 1963 |
| Irdeto UK Limited | Information & communication | 2006 |
| Iriusrisk Ltd | Information & communication | 2019 |
| IRS Corporate Limited | Hospitality | 2007 |
| Isis Rescue Limited | Wholesale & retail | 1996 |
| Isleworth Industrial Estate Freehold Limited | Real estate | 2022 |
| Itda Limited | Administrative & support | 2003 |
| ITL Health Limited | Wholesale & retail | 2008 |
| ITT Consultancy Ltd | Professional & scientific | 2018 |
| Iverna Holdings Ltd | Financial services | 2021 |
| IWA Advisors Limited | Other services | 2022 |
| Izzybee Ltd | Wholesale & retail | 2018 |
| J a. Lloyd Carpentry Ltd | Extraterritorial | 2025 |
| J B Sinclair Limited | Professional & scientific | 2001 |
| J D Environmental Services Limited | Administrative & support | 2025 |
| J D Stuart Consulting Services Limited | Professional & scientific | 2023 |
| J H Marketing (Africa 2000) Limited | Wholesale & retail | 2000 |
| J P Hildreth Ltd | Professional & scientific | 2006 |
| J. C. Frost & Co. (Holdings) Limited | Real estate | 1989 |
| J.A Properties & Land Development Ltd | Construction | 2010 |
| J.C. Frost & Co (Burnham) Limited | Real estate | 1995 |
| J.C. Frost & Co Executive Rentals (Windsor) Ltd | Real estate | 1990 |
| J.C. Frost & Co. (Gerrards Cross) Ltd | Real estate | 1991 |
| J.C. Frost & Co. Surveyors (Thames Valley) Limited | Professional & scientific | 1995 |
| J.R. Stevens & SON Limited | Wholesale & retail | 1976 |
| Jaaames Ltd | Arts & recreation | 2020 |
| Jack C Williams Limited | Construction | 2012 |
| Jade Ventures Global Limited | Financial services | 2024 |
| Jaggard Macland LLP | | 2011 |
| Jaia Developments Ltd | Construction | 2025 |
| Jake Murphy Financial Planning Limited | Professional & scientific | 2022 |
| James & Wallis Limited | Wholesale & retail | 1978 |
| James Lane Solutions Limited | Professional & scientific | 2015 |
| James Milligan Limited | Professional & scientific | 2023 |
| James Street Finance Limited | Extraterritorial | 1988 |
| Jammable Limited | Information & communication | 2023 |
| Jampee Thai Limited | Hospitality | 2023 |
| Jansons Investment Group Limited | Administrative & support | 2018 |
| Jarmes Limited | Wholesale & retail | 2024 |
| Jarrett Consulting Ltd | Professional & scientific | 2007 |
| Jarrett Fencing Limited | Professional & scientific | 2016 |
| Javelin Software Ltd | Information & communication | 2025 |
| Jazzee Blue Publishing Limited | Information & communication | 1995 |
| Jazzee Blue Records Limited | Information & communication | 1995 |
| Jazzee Blue Studios Limited | Information & communication | 1995 |
| JB Capital Ltd | Real estate | 2007 |
| JBE Search Limited | Administrative & support | 2018 |
| Jeannette Properties Limited | Real estate | 2021 |
| JEB Trading Ltd | Financial services | 2007 |
| JEN Siebrits Consulting Ltd | Professional & scientific | 2025 |
| Jenus Properties LLP | | 2003 |
| Jeremy B Gwilt Limited | Information & communication | 2015 |
| Jewell Homes Ltd | Real estate | 2021 |
| Jfan UK Ltd | Manufacturing | 2017 |
| JIB Woodwork Ltd | Construction | 2025 |
| JJN Design & Build Ltd | Manufacturing | 2021 |
| JK & J Investments Ltd | Wholesale & retail | 2022 |
| JK Juice Company Limited | Manufacturing | 2024 |
| Jkcb Solutions Limited | Health & social care | 2021 |
| Jmac Consultancy Ltd | Information & communication | 2022 |
| JMJ Property Limited | Real estate | 2015 |
| JOE Corrie Coaching Ltd | Arts & recreation | 2025 |
| JOE Corrie Nutrition & Lifestyle Ltd | Arts & recreation | 2025 |
| Joffe Investments Limited | Real estate | 2016 |
| John Adey Properties Limited | Real estate | 2019 |